The present invention relates to a snubber with integral test structure.
By way of background, in the commercial power industry hydraulic snubbers are used in plant to mount and support pipes, steam generators, and other equipment relative to fixed structures such as walls. The snubbers permit relatively slow gradual movement between such mounted equipment and the fixed structure, but in the event the mounted equipment is subjected to an abrupt shock, the snubbers will effectively lock up to prevent abrupt relative movements which could result in damage of the mounted equipment.
By way of further background, the snubbers used in nuclear power plants usually require an annual inspection which tests their various physical characteristics including drag, lockup and full load pressure characteristics. Drag is the force required to overcome the friction experienced when moving the piston of the snubber. Lockup is the shock force at which the piston will not move relative to its cylinder. Full load pressure characteristic is the pressure which the hydraulic fluid can be subjected to at full load without accompanying seal leakage or parts breakage.
One way of testing in the past was to bench test by removing the clevis pins at the ends of the snubbers which connected them between the mounted equipment and the fixed structure, decontaminate the snubber if it was in nuclear containment, and thereafter put it into a mechanical tester and test it at the required velocity to get it to lock up, and to test it for friction to see whether it would stick or bind, and to test its full load output in a large press to determine whether there was any seal leakage or parts leakage. The testing included connecting a first chamber on one side of the piston to a high pressure fluid source and connecting a second chamber on the other side of the piston so that it could be exhausted. Thereafter, the pressure in the first chamber was increased gradually to determine the force required to overcome friction, the pressure was then increased abruptly to determine whether the snubber would lock up, and thereafter the piston was moved to the limit of its travel and the pressure was increased to a predetermined high value to test its full load characteristics, which included whether the seal in the first chamber would leak. Thereafter, the fluid connections to the first and second chambers were reversed and the foregoing tests were repeated. The work required to prepare the snubbers for actual testing was obviously very time-consuming and expensive.
Another prior method of testing the snubbers was to support the snubber, which could weigh up to about three tons, from underneath with a large jack, disconnect one clevis by removing its pin, and retracting the jack to drop the disconnected end of the snubber. Thereafter, it was tested in the same manner described above. While this procedure was an improvement over the earlier procedure which required decontamination, it still was subject to certain shortcomings, namely, that the snubber had to be disconnected and lowered by the use of a jack. Furthermore the procedure was rather time-consuming and, in addition, many snubbers, once installed, were not readily accessible so that a jack could be used to lower an end thereof after the snubber clevis had been disconnected. Accordingly, this required the still-connected snubbers to be tested in place, without disconnecting the clevis pins, which could result in breakage of the mounted equipment, especially considering that the snubbers had to be tested at full load, in accordance with testing requirements.